Getting the whole population to believe in the nation’s wars, and be willing to sacrifice themselves, is an enormously powerful idea.

Mass mobilisation is the social and political theory that claims that the general public can be inspired to fight for a country or for nebulous ideals such as “freedom”. When men go willingly to war they can be persuaded to suffer hardships beyond those of regular soldiering: overcoming a lack of supplies, food and arms are part of the struggle. Belief is a powerful tool in battle: men will stand for an idea, even in the face of death. Mobilisation reduces the recruitment costs for militia units.

Historically, the French Revolution was the first example of mass mobilisation, even if it was not referred to as such at the time. The people were harnessed to the ideals of the revolution, and willing to undergo hardships in its name. As these ideals were threatened by foreign monarchies, the people could be easily roused to defend them. Patriotic and revolutionary fervour was encouraged by the government to great practical effect; by 1799 more than one million men had shown themselves willing to fight for France and the Revolution.

Mass Mobilisation grants a small decrease in the cost of training line infantry and militia. Depending on how many infantry a faction recruits, this can potentially save hundreds of gold over the course of a game (a line infantry regiment costs between 300 and 700 gold, depending on type and existing discounts), which isn't too significant but can potentially allow for a unit to be recruited or a building upgraded a turn or two earlier. Mass Mobilisation grants a larger discount to militia units, but as they don't cost much to begin with this isn't too significant either.

Arguably the more significant benefit of Mass Mobilisation is its unlocking the ability for generals to Inspire Units. This is separate from the similarly-named "inspire nearby units" trait that most elite infantry and generals have, and instead is a manually activated ability.

Finally, researching Mass Mobilisation is required for building Drill Schools, unlocking more advanced technologies down the military technology tree.